1. Field of the Invention
This invention relates to a solution for determining the growth of trees based on measurement data obtained at two different moments of time. Such measurement data can be obtained for instance by a laser scanner located above the trees.
2. Description of the Prior Art
Previous solutions for measuring the growth of trees are based on field measurements from the ground. Measurement equipment is thus transported to the location of a specific tree at two different occasions and the diameter or the height of the tree is measured from the ground. The obtained field measurement results are then compared to each other in order to determine the growth of the tree in question.
The above described prior art solution has the drawback that it is very slow. The number of trees which in practice can be measured is relatively small due to the time needed and costs involved in carrying out measurements.
Previously, for instance from WO-publication 01/31290, a solution is also known for obtaining a three-dimensional measurement result of stand attributes of trees located at a predetermined area. In this known solution, an aircraft, such as an airplane or a helicopter, is provided with measuring equipment which includes a laser scanner. Processing of the information obtained by the measuring equipment makes it possible to determine the size of the trees. This solution makes it possible to measure the size of a large number of trees during a relatively short period of time. So far, however, nobody has been able to disclose a solution for growth determination of trees where this known measurement solution is utilized. A significant problem has been the inaccuracy involved in the measurement. Present state of art methods do not utilize multi-temporal datasets in laser scanning. Even the use of pixel-based change detection methods and multi-temporal laser data sets will result in inaccurate growth estimates.